Efficacy of chromocult coliform agar for coliform and Escherichia coli detection in foods

Abstract

Chromocult coliform agar (CCA) was compared with Petrifilm Escherichia coli count plate (PEC) for identifying coliforms and E. coli in a variety of meat products. Products examined included 45 raw beef samples, 12 sausage emulsion samples, 11 samples of meat-based ready-to-eat appetizers, and 8 pork trimming samples. Coliforms from CCA and PEC were confirmed by gassing in brilliant green lactose broth plus a positive reaction on purple broth agar plus lactose after incubation at 35°C for 48 h. Lauryl sulfate tryptose plus methylumbelliferyl-β-glucuronide and tryptophan broth were used to confirm E. coli from CCA and PEC with 48-h incubations at 35 and 42.5°C, respectively. API 20E test strips were inoculated for final confirmation. The overall respective confirmation percentages (CFU/g) for the PEC and the CCA methods were 93.1 and 93.7% for coliforms and 99.8 and 98.1% for E. coli, although the CCA method yielded significantly (P < 0.001) higher mean CFU/g values for both coliforms and E. coli. Regression analyses of these data indicated a strong positive linear relationship existed between the two methods over a wide CFU/g range for both coliforms and E. coli. The respective correlation coefficients obtained for coliforms and E. coli of 0.89 and 0.86 indicate that the CCA method provides a reliable optional method for these determinations in meat products.